While there is no "forever free" version of OctaneRender for Cinema 4D R26, you can access the official OctaneRender Demo for free to test system compatibility and learn the interface. This demo is fully functional but includes watermarks on final renders and limits on output resolution. Official Access & Free Options
You're looking for information on Octane Render for Cinema 4D R26 and possibly a free download. Here's what I found: Octane Render Cinema 4d R26 Free Download
Once you have downloaded the installer from the official OTOY website: While there is no "forever free" version of
System Requirements